ThinkPads beep during certain key combinations – found the cause

I’ve had an annoying beep on my thinkpad whenever I tried to write CD quickly.

It particularly shows when you press these three keys at the same time:

Shift+CD

Recently, I googled for the symptom to find out the cause.
Below are a few links I found, but this is the actual cause (thanks Kriston!):

It has to do with certain keyboards and their buffers which cannot handle multiple key combinations on the same “channel.”
The beep is caused by the keyboard raising an error signal to tell the computer to notify the user of the missed keystroke.
This is a very old problem that keyboard makers are often ignorant of.
Today it is a real problem for some of the more popular, high-priced “elite” USB keyboards on the market.
Many of these cannot handle more than three keystrokes on the same channel, similar to the Lenovo keyboards, but unlike the Thinkpad, the “beep” does not occur and you have a silent error introduced while typing quickly.

So this is what happens:

You press three or more keys that all fall in a certain channel

The ThinkPad keyboard finds out you potentially loose a keystroke and sends a beep signal to the system.

The system has a Beep Service which plays a beep through your speaker

Knowing this, I’m glad it beeps: it advices me that I just might have lost a keystroke.

If you are annoyed by the beep, and don’t mind loosing a keystroke one in a while, you can disable the beep service.
There are similar steps if you run Linux on your system.